The present invention relates to electrical transformers and, more particularly, my invention relates to inverter type ferrite core transformers of the type containing a plurality of fractional or single turn secondary windings, to the method of manufacturing such windings and to supporting the transformer in the combination of an electrical device.
The transformer is a known electrical component which contains at least two electrical windings formed into a coil or coils mounted on a core of magnetic material by means of which AC electrical energy is coupled from one winding to the other, respectively termed the "primary" and the "secondary". Generally each of those windings are formed of a large number of turns of electrical enamel coated wire fabricated in the form of a coil by means of conventional coil-winding machinery. Thereafter in the assembly of the transformer the formed coil is mounted to the core of magnetic material. Generally, the voltage relationship between the primary winding and the secondary winding or windings is governed in great part by the "turns ratio"; the ratio of turns in a secondary to the turns of the primary. Where the ratio is greater than one a "step-up" voltage relationship exists and where less than one, a "step-down" relationship exists. By design a transformer may contain one or the other or both step-up and step-down windings. Each of these prior art structures permit of many variations and methods of manufacture which are widely known in the industry and in the patent literature, to which the reader may make reference. By way of further background it is recalled by those skilled in this art that manufacture of electrical coils for transformer application involves winding of the coil on coil-winding machinery, using typically enamel coated wire, and involves set-up procedures requiring time and labor. In many transformer coils the beginning, tap and end turns of the enamel coated wire windings are connected to separate electrical insulated jacketed leads respectively, to form the circuit connections by means of which the transformer windings are connected electrically to other circuits. In other structures the end leads may be connected to electrical terminals built into coil bobbins used in connection with some transformers of more expensive structure so that the transformer may be easily "plugged-in" to a printed circuit board. In one type of electronic device, namely a solid state inverter-oscillator type circuit, for operating one or more gaseous discharge devices, such as a fluorescent lamp of the rapid start type, circuitry is included for converting either low voltage DC or AC line voltage of low frequency, typically 60 hertz, to the high-voltage high-frequency energy supplied to the lamp, as well as to provide low-voltage current to the lamp's heaters. This electronic device includes a transformer containing a primary winding and a plurality of secondary windings which are located on a core of magnetic material, such as the conventional ferrite core material useful at high frequencies or magnetic steel laminations formed into a transformer core. Although a high-voltage secondary winding is required containing a large number of turns of enamel coated wire efficiently assembled by high speed coil winding machinery, other secondary windings intended in the apparatus to provide the heater currents at low voltage to the fluorescent lamp cathodes, require only one or two turns at most. In the case of a solid state ballast intended to operate two rapid-start type lamps, for example, there is a requirement for three such low voltage heater windings consisting of a single wire turn, at least one additional low voltage winding for which a single wire turn supplies satisfactory voltage, and a further secondary winding intended to supply electrical components within the device requiring only two turns of wire. In other applications a fractional turn winding of 1/2 turn or 3/2 turns is all that is required. As the reader familiar with the methods of transformers manufacture can appreciate, to accomplish winding manufacture according to the one existing procedure would require the winding and insulation of a plurality of single turns of wire which, if enamel wire were used, may require the attachment of electrical jacketed leads, as described above, or to alternatively wind the individual one turn windings with insulation jacketed wire. Obviously a certain amount of time and effort is involved in handling a number of these low voltage secondary windings and this time and effort accordingly is equated with unnecessary expense in manufacture and is necessarily reflected in the price of the product. A higher price for a product in turn acts to limit its marketability, even though the product is technically innovative and possesses attractive advantages, if the cost of obtaining those advantages is too great in comparison to conventional or old methods of obtaining the essential functions performed by the product. Specifically, by way of example, the solid state type of fluorescent lamp ballast possesses many advantages over the conventional electromagnetic type for which it may serve as a substitute. The present cost of such solid state ballast, however, is one factor that has heretofore limited marketability since in the minds of many potential buyers the additional cost exceeds the additional benefits from such substitution.
My invention simplifies the winding structure and assembly of transformers having some secondary windings containing but a fractional or small number of turns and thereby reduces the cost of manufacture of solid state inverter type ballast incorporating a transformer, and, more particularly, reduces the cost of manufacture of the transformer as a major advantage. A related object is to provide a transformer containing a plurality of single turn windings and a method of manufacturing same without the necessity of separately handling individual turns. A still further aspect of the invention is to provide a transformer winding structure which assists in supporting the transformer upon a printed circuit board.